Describing the Movement of Water in Earth's Atmosphere

Lesson 3 Exploration 2Objective:

You will learn how water is constantly moving and cycling in the Earth system.

Earth's Atmosphere Earth's atmosphere contains nitrogen, carbon dioxide, oxygen, and water. At any given time, there is enough water in the atmosphere to completely fill Lake Superior, the largest lake in North America.

How Water Reaches the Atmosphere

Water can exist in the atmosphere as a solid, a liquid, and a gas.

The processes that move water into the atmosphere:

Evaporation

Transpiration

Sublimation.

Sublimation

When water changes directly to water vapor without first becoming a liquid, the process is called sublimation. Energy is required for this process to occur because the molecules of solid water must gain enough energy to break free from the solid state. Less than 1% of the water in the atmosphere comes from sublimation.

Transpiration

Plants release water vapor into the environment. As water flows through a plant, some water changes to water vapor as it leaves the plant through small pores. This release of water vapor into the air by plants is called transpiration.

This process requires the addition of energy to the water molecule so they can break away from the liquid state.

About 10% of the water in the atmosphere comes from transpiration.

Transpiration Experiment

Evaporation

When liquid water gains enough energy to escape the liquid’s surface and form water vapor, the process is called evaporation. Some water evaporates from the water on land. However most water evaporates from the surface of Earth's oceans. About 90% of the water in the atmosphere comes from evaporation of Earth's liquid water especially ocean.

Water in the Atmosphere

Water molecules in the atmosphere are in constant motion, bouncing against each other and against other gas molecules in the air. During these collisions, the water molecules can gain or lose energy. If a water molecule collides with a molecule that is warmer than it is, the water molecule gain energy. If a water molecule collides with a molecule that is cooler, the water molecule will lose energy.

Condensation and CloudsAs air cools, water vapor in the air may change to a liquid from a gas in a process called condensation. As water molecules bump into each other, they can stick together and form small water droplets or ice crystals, depending on the air temperature. At first, these droplets form around tiny particles in the air, such as sea salt, dust, and pollen. (Condensation Nuclei)

.As more and more water molecules collect together the droplets become larger. When there are enough water droplets, visible clouds, fog, or mist forms.

PrecipitationWhen gravity pulls water towards Earthś surface.

Rain: water

Snow: forms when the water in clouds freeze; 6 part frozen crystals

Hail: forms when the water in clouds freeze; frozen balls of precipitation

DepositionOccurs when water vapor changes state directly from a gas to a solid. Happens high on mountains where the temperature is so low. Water vapor forms snow without becoming a liquid first.